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Some TeX History
[This short TeX History is excerpted from First Steps With General Typesetting by Richard Koch, If you have latest TeX Live with TeXShop, you can find the full version of this short course on its Help menu. I have been through a long detour from CTeX to LaTeX CJK packages by Werner Lemberg, and at last settle down to XeLaTeX! ]
TEX was invented before several of the important computing developments of the twentieth century. In 1978 there was no Macintosh and no generally available computer with a graphical interface. Personal computers printed output using a single bitmapped font in which all characters had the same width; some computers only printed upper case letters.
Consequently, Knuth had to invent outline fonts at the same time that he invented TEX. In his documentation, Knuth always talks about two programs, the typesetting program TEX and the outline font program MetaFont.
Later in the decade, other players introduced their own outline fonts using different formats: Adobe's Type 1 Postscript fonts, Apple's Truetype fonts, and Microsoft's OpenType fonts. The history of these fonts is rather complicated; suffice it to say that each is now supported on the Mac and available on other operating systems as well. A vast number of beautiful fonts are available in these new formats.
Adapting these fonts for use in TEX is a complicated task, which has only been successfully completed in a small number of cases.One of the most important complaints about TEX is the limited number of available fonts.
XEX LAT X and Fonts
XELAT X completely solves the font problem.
It can use Knuth's fonts, of course, but it can mix these with system fonts in Adobe Type 1, Truetype, and OpenType formats. These fonts need not be adapted for use in TEX; instead they are immediately available.
TEX source manuscripts contain standard characters available on any typewriter. Indeed, originally TEX could only accept the 128 standard ASCII input characters. Later this was expanded to 256 characters. This is enough for standard English and for Western European Languages, but it is certainly not enough for Japanese, Chinese, and a multitude of other languages. Over the years, many projects have attempted to adopt TEX so it can typeset these other languages.
Later the same problem arose in the entire computer industry, since a large number of sales occur in countries which do not use Western scripts. The solution invented by the industry is Unicode, an open standard which can theoretically encode the characters of all languages on earth. Most computer manufacturers have adopted this standard. For example, the edit class in Cocoa (and consequently TeXShop's editor) accepts arbitrary Unicode characters.
XELATAX and Unicode
XELATAX modifies TEX to accept any Unicode code character; source documents are saved in UTF-8 Unicode format. In conjunction with full support for OpenType fonts, this makes it possible to write TEX documents in virtually any language on earth.
If you want to write in Chinese, Japanese, or any other languages beside English and European languages, then XeLaTeX is going to make your life much easier. For English writers, the main benefit of XeLaTeX is the ability to use the fonts on your computer, just as you can with MS Word or other similar word processor softwares.